c4-toy

My base 991 7sp MT with standard exhaust and single oval tips makes a pretty good exhaust growl inside the cabin with sport button turned on (sound symposer which i personally like), not sure how it sounds on the outside on the street. My question is this... is there a way to get a bit more growl out of the exhaust without too much expense or modification to the stock exhaust? someone mentioned in another post "opening up the side mufflers or pipes" not sure what that means exactly. Appreciate any comments. Thx

K-A

Aww, that awesome sound I heard in the 991 Carrera I drove was partially synthesized? That's a bummer. It was pretty damn loud in Sport though, so I guess it's a good thing that it could be "synthetically" turned down if it gets annoying sometimes. It would be nice it if does sound like that outside of the car though. The one I drove seemed to have a nice characteristic "911" sound from outside at idle.

rijowysock

it's a "gundo hack" (partial side muffler bypass) which is basically what the "S" exhaust does (i'm very impressed they are doing this now) (also basically what PSE does when "open")

the exhaust flow under natural pressure travels thru the muffler and is muted as usual, at higher RPM's/pressure the exhaust now looks for other routes that have less backpressure and some of the exhaust then bypasses the restrictive muffler and travels thru said bypass and out the tips.. you will notice some low end loss due to less backpressure but mid range gains and top end around the same.

standard side muffler:


muffler with bypass (excuse my weld job):


the bypass makes it sound just like the 991 "S" exhaust on how it bypasses some of the exhaust directly out the back.. doesn't void any warranties (porsche voids warranties if the cat's are messed w/) adding "pops" and "burbles" to the stock exhaust is amazing.

the biggest improvement after the side bypass would be a new center pipe bypass (think of the X pipe they had for the 997.2).. this made the DFI engine's sound just like the previous 997.1 engines that had PSE... but nobody has really created a center bypass at an affordable price...

most if not all will be happy with the "gundo hack" and shouldn't cost more than $250... the center pipe bypass should be added in conjunction with the above hack to get the best sound.. (those bypass's being made are asking for 750/1k)







it's not synthesized, it's all real but the added sound (deep end of it) comes from the intake noise which is why it's the same throughout rpm's but changes on throttle amount.

outside the car sounds like a kitten, i was very frustrated when hearing it myself... my 07' G35 coupe had a much better sound... but then again the 997.2 also was very calm'd down off the lot. (the DFI engine has much more restrictive cat's to create back pressure to help alleviate known issues w/ DFI)

my 997.2 with the hack and center bypass=sounded amazing, just like my 997.1 with only the side muffler hack.

K-A

Ah, good to know that it's not synthesized, like that joke of a concept they've done with the new M5.

Unfortunate to hear that it sounds so tame or puny outside though. Is it the engine itself that just has a tame tone, or all the muffling? Also, of course the S sounds better I'm sure, is it a LOT better, or just a little better sounding?

As for losing back pressure, it's definitely an unfortunate side effect of freeing up exhaust noise/flow, especially on smaller cylinder-d cars. The Carrera Base that I drove felt very quick and peppy, but my only "knock", if I could even reach for one, was some lack of low end torque which made first and second gears feel a little bogged down and long. Would hate to enhance that by releasing backpressure.

rijowysock

obviously it's the restrictive exhaust, exhaust makes (or doesnt) make all the sound...

the S engine sounds almost identical, the difference is the exhaust, both models have very free flowing headers... very restrictive cats.. the difference is after the cats.. the S model exhaust goes into the center muffler, half exits directly then thru the tips, the other half thru the side mufflers and then to tips.

the base goes to side mufflers and out, no bypass..

the cars already have low tq, it's not a big engine.. both cars powerband has changed since 997 and has more power up top.. the loss of tq from opening up the exhaust is minimal but slightly felt... maybe 10lbs if that. it's not much at all.

the car itself doesn't wake up until the high RPM's and is designed that way on purpose... just the nature of the powerband.. and is the same on both models..



keep in mind, the opening the side mufflers is exactly what the S model already does... and what the PSE does.. keep in mind the PSE closes up down low to keep a little pressure..


id do the "hack" again without any question or concern... and if i still had the car i would develop my own center bypass without waiting for a company to do so... and the car would sound amazing but not over the top.

K-A

Good info, thanks.

The Base engine sounding almost identical to the S engine makes me happy to hear. Then some exhaust tweaks if you want it louder and you're good to go.

Ah yes, the historic upper powerband power of a 911. Very characteristic of the car. I've always been a torque guy but I appreciate how the 911 has it dialed down. In the upper RPM's, I found the non-S to be very responsive and exhilarating, especially for one like me who's a pretty tame driver usually stuck in traffic. The sound in the cabin from the non-S when you get in those upper RPM's was race-car-esque IMO, it really screamed at had that characteristic "911 motor right behind your a$$" experience that you won't find anywhere else.

c4-toy

This is great, how does one get this "gundo hack" done, is this something a reputable speed shop can do or dealer? Would love to hear the before and after sound.
Another question is can the already bi-passed side mufflers of an S exhaust be retrofitted on the base eliminating the need to replace the entire exhaust or do the "gundo hack"if that makes sense.

brianja

Can you elaborate on this statement, please?

I've had direct injection carbon buildup problems on my current Audi RS4 (as has everyone). The 991 being DFI is a concern of mine. I would love to know what Porsche has done to address the potential issues.

Thanks.

rijowysock

any muffler shop can do it, if you bring the mufflers off the car so they dont know it's porsche it will probably be $100... if you bring them on the car.. 250-400$... it's just welding.. and the side cans come off VERY easily.. if you want to attack removing them after calling a muffler shop to see if they can weld some stuff on your exhaust.. ill walk you thru it... can remove w/o removing bumper.. they just fall out..

the S side mufflers are identical to the base... the difference is the center muffler... you would need a lot of stuff to make them work cause diff tips and diff brackets on the side mufflers...

if you bought the S stuff, you would need everything.. i got contacted by someone once who had it for sale/available but never asked price cause my car was sold..

do the hack, benefit is some dont want to have someone weld their cans so if u didn't want it someone will always swap you for stock...

i'm not a big engine person but when i had my 997.2 i went into detail with a tech about the exhaust before modifying, he said many cars have the build up... but the cure is additional backpressure.. the 997.2 had something like 4 cat's on it which added tons of backpressure.... from what i have been told no issues have been seen on 997.2 w/ buildup and some people have over 100k miles..

the 991 exhaust has the same super duty cat's but much free'er flowing headers...

all i know is the tech was from germany investigating some problems with a 997.2 GT car and he went into super detail about the engine design and how the DFI was better in almost every way but people would obviously be upset about the loss of the old engine... so on and so forth but with all the regulations and strict this and that it will all be DFI soon.

cmb13

Revisiting this thread. Has anyone attempted this on a 991?

edmovi

I've done the gundo hack to my 991 and it doesn't sound quite as nice as the PSE (not as mucho pop and burble) but better than before.

cmb13

I might try it. I just want a little more sound, not too loud. No drone?

edmovi

No drone and not too loud either. I wouldn't mind if it was a little louder. It's not as loud as the PSE. My son, his friends and my friends love the sound. My wife on the other hand, when she was standing behind the car when I stared it cold, asked if the exhaust was broken :-)

The sound inside the cabin is a little louder than before, but a little quieter than with the sport button activated. When the sport button IS activated the combination of both is great. I can send you a sound file if you want.

chuck911

This is a different approach, but for people more concerned with the sound inside vs what people hear outside, there was a thread several months ago showing how to remove sound deadening material from the rear deck just below the rear window. Nice things about this: its free, its restorable, it doesn't annoy neighbors. In similar manner its possible to fine tune the sound symposer, which is really just a tube going from the intake to the cabin with a membrane in between to keep odors out.

cmb13

I saw that thread also. Wouldn't that create more undesirable road noise in addition to the desirable engine sound?